【作者】 张海民；

【导师】 全燮；

【作者基本信息】 大连理工大学 ， 环境工程， 2008， 博士

【摘要】 传统TiO₂光催化氧化技术在催化剂应用形式方面存在诸多不可克服的制约因素，如粉末光催化剂容易流失、分离回收困难、固载后光催化活性降低等。为了克服单个处理技术存在的不足和缺陷，将光催化技术与膜分离技术（或电化学技术）耦合可从不同角度很好地解决此类难题。为此，应用溶胶-凝胶法以不同无机膜作为载体制备了集光催化和膜分离一体化功能的TiO₂复合分离膜；应用阳极氧化法和水热合成法制备了TiO₂纳米结构膜电极，并对随后TiO₂光催化复合分离膜和TiO₂纳米结构膜电极在耦合工艺条件下的性能进行了系统地调查和研究。本论文围绕以上研究内容，主要开展了以下几个方面的工作：（1）应用溶胶-凝胶法，以管状ZrO₂无机膜为载体制备了无开裂的TiO₂／ZrO₂复合分离膜。实验结果表明，通过控制溶胶中PEG（2000）的添加量及涂膜次数，我们能够很好地控制随后TiO₂／ZrO₂复合分离膜的孔径，进而达到控制复合膜通量和截留率的目的。实验发现，溶胶中添加1.0g PEG（2000），5次涂膜制备的复合分离膜对不同分子量PEG的截留都较低，这主要归因于所制备的复合膜孔径较大（100～200 nm）。以染料直接黑168作为模型污染物（100 mg/L），实验运行400 min后，通过光催化和膜分离耦合技术，染料的去除达到52％以上，对比单独膜分离（20％）及单独光催化（35％）操作明显提高。但是因为所制备的复合膜孔径较大、采用外压式十字流过滤方式污染物与TiO₂光催化剂接触时间较短及反应器设计上存在的问题等，因此即使通过耦合工艺染料的去除还没有达到理想的效果。（2）应用溶胶-凝胶法，以Al₂O₃无机膜片（平均孔径200 nm）作为载体，制备了孔径为50～100 nm的功能性TiO₂／Al₂O₃复合分离膜，用染料直接黑168和酸性橙Ⅱ作为模型污染物，采用抽真空提供过滤驱动力的方式，对复合膜的截留能力、光催化能力及耦合2种技术处理染料的能力进行了考察。XRD分析表明，复合膜中TiO₂粒子的平均粒径为22 nm，其中锐钛矿相占86％，金红石相占14％。在有H₂O₂辅助的条件下，通过耦合工艺处理400 min，直接黑168的去除效率达到84％，与单独光催化（73％）和单独膜分离（64％）相比较，这种耦合工艺使染料去除效率明显提高。耦合工艺条件下复合膜6次重复使用实验表明，染料的去除效率可保持在65％以上，且复合膜孔结构稳定，没有明显地损坏，稳定性较好。（3）应用溶胶-凝胶法，以Al₂O₃无机膜片（平均孔径200 nm）作为载体，制备了孔径为1.4～10 nm的Si掺杂TiO₂／Al₂O₃复合分离膜，用染料直接黑168和表面活性剂十二烷基苯磺酸钠（SDBS）作为模型污染物，采用抽真空提供过滤驱动力的方式，对Si掺杂复合膜的截留能力、光催化能力及耦合光催化和膜分离工艺处理污染物的能力进行了评价和考察。实验结果表明：Si的掺杂，一方面提高了复合膜的热稳定性，从而抑制了复合膜中TiO₂从锐钛矿相向金红石相转换及TiO₂晶粒的生长（保持在7.0 nm左右），这对提高随后复合膜的机械稳定性和光催化活性具有重要意义。另一方面，Si掺杂复合分离膜在紫外光照射下具有优异的表面亲水特性，这对预防膜污染、提高膜通量具有重要意义。应用20％Si-TiO₂／Al₂O₃复合分离膜，通过耦合工艺，直接黑168的去除效率达到85％以上，SDBS的去除达到89％，对比单独的光催化和膜分离都明显提高。此外，在有UV光存在时，Si掺杂复合分离膜稳态渗透通量对比没有UV光时提高了将近9 L／m²·h。以上实验结果都表明，20％Si-TiO₂／Al₂O₃复合分离膜同时具有光催化、膜分离、预防膜污染和提高膜通量的多功能。两种技术耦合后，具有明显地耦合协同效应。（4）应用阳极氧化法和水热合成法，以金属钛片为基体，制备了TiO₂纳米结构电极。光电化学实验结果表明，TiO₂纳米管阵列电极的光电流响应主要由纳米管管壁横截面积决定（即有效电极光照面积）。电极的光电催化反应电阻(R=k/J_sph+R₀=R_I+R₀)通过简单的光电化学方法测定，用来表达纳米管电极的光电子传输特性。其中，变化的电阻成份（R_I）被发现与电极的饱和光电流成反比，其值依赖于实验条件（如光强等）；不变的电阻成份（R₀）是纳米管电极的一个内在特性，它代表了TiO₂催化剂晶体边界及催化剂与基体界面之间欧姆接触电阻的总和；k值大小代表了光电子从TiO₂光催化剂层中去除的难易程度。电解质溶液pH变化能够影响纳米管电极表面所带基团物种种类及光电子存在的能级状态，因此影响了最终TiO₂纳米管电极对水和有机物的光电催化活性。通过控制水热合成条件，分别得到TiO₂纳米管和TiO₂纳米带膜电极。所制备的纳米结构电极在光电催化氧化水、有机物和染料敏化太阳能电池（DSSCs）中都有很好地应用。总之，这些纳米结构电极的获得不但可以解决TiO₂粉末光催化剂易流失、回收难的问题，还可以通过光电耦合技术提高电极的光催化活性。更多还原

【Abstract】 Several intrinsic drawbacks exist in the conventional TiO₂ photocatalytic oxidation process in terms of the application forms of photocatalyst, e.g., powder photocatalyst loss, separation, recovery, and decrease in photocatalytic activity after TiO₂ immobilization, which can be overcome effectively by using photocatalytic membrane reactor （or nanostructured electrodes）, directly coupling the photocatalytic oxidation process with the membrane separation technology （or the electrochemical technology）. Therefore, TiO₂ composite membranes with both photocatalytic capability and separation performance have been fabricated using different inorganic membranes as substrates by a simple sol-gel technique, and TiO₂ nanostructured film electrodes have been prepared by anodization and hydrothermal reaction methods. The resulting TiO₂ photocatalytic composite membranes and TiO₂ nanostructured film electrodes were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and UV-vis diffuse reflectance spectra （DRS） and so forth, and their performances under coupling technologies were investigated and evaluated detailedly. In this dissertation, the following several parts of work have been done:（1） Crack-free TiO₂/ZrO₂ composite membranes on ZrO₂ supports have been successfully fabricated from TiO₂ sols by a simple sol-gel technique. The pore sizes of the prepared TiO₂ composite membrane can be effectively controlled by adjusting TiO₂ sol viscosity, the amount of polyethylene glycol （PEG）, and calcination temperature of composite membrane, and thus controlling permeate flux and retention of the resulting TiO₂ composite membrane. The experimental results demonstrate that the retention of TiO₂/ZrO₂ composite membrane （1.0 g PEG 2000, 5 coating cycles） is not high （e.g. the retention of 67% for PEG 20,000）, which is due to the larger pore sizes of composite membrane （100-200 nm）. By coupling photocatalytic process with membrane separation technology, the removal efficiency of Direct Black 168 （100 mg/L） was improved obviously, being 52% within 400 min, while the values were 20% and 35% with membrane separation alone or photocatalysis alone during the same time, respectively. Lower removal efficiency of dye under coupling technology is ascribed to the larger pore sizes of composite membrane, the shorter hydraulic retention time, and the shortage of the design of reactor.（2） TiO₂/Al₂O₃ composite membranes with both photocatalytic capability and separation performance have been fabricated by simple sol-gel technique. Pore sizes of the resulting composite membrane were mainly controlled by the TiO₂ sol properties and immersion time. XRD patterns indicate that anatase of TiO₂ in composite membrane is dominant phase （86%） and TiO₂ particle size is about 22 nm. In order to obtain high removal efficiency of dye, some operational parameters such as the pressure difference, the initial pH, and air flow were investigated and discussed. By coupling technology, the removal efficiency of Direct Black 168 can reach 84% within 400 min, while the removal efficiencies are only 73% and 64% using photocatalysis alone or membrane separation alone, respectively. In comparison with photocatalysis alone or membrane separation alone, the removal efficiency of dye was improved obviously by coupling technology. The results of TiO₂ composite membrane after being used 6 times by coupling technology show that the pores structure and morphology of the composite membrane have no significant change and damage compared with before being used, and the removal efficiency of dye can be kept at above 65%.（3） Si doped TiO₂/Al₂O₃ composite membranes have been successfully fabricated from SiO₂/TiO₂ sols using porous Al₂O₃ support membranes. XRD patterns confirm that the embedding of amorphous SiO₂ into nanophase TiO₂ matrix helps to increase the thermal stability of TiO₂ which suppresses the phase transformation from anatase to rutile and decrease the size of TiO₂ particles. Moreover, the surface of 20%Si-TiO₂/Al₂O₃ composite membrane with pore sizes of 1.4-10 nm exhibites extremely high affinity for water under UV irradiation with water contact angle decreased from 62°to nearly 5°within 80 min. By coupling membrane separation with photocatalysis technique, the removal efficiency of Direct Black 168 was improved remarkably; being 85% within 100 min, while the values were 66% and 73% with photocatalysis alone or membrane separation alone during the same time, respectively. Similar results can be obtained using sodium dodecylbenzene sulfonate surfactant （SDBS） as test pollutant. Good photocatalytic activity and wettability of composite membrane under UV irradiation help to obtain high permeate flux across the composite membrane. The above results indicate that the Si doped TiO₂/Al₂O₃ composite membrane have the multifunctions of separation, degradation, and improvement of membrane flux in photooxidation of organic contaminants in wastewater.（4） TiO₂ nanostructured film electrodes have been prepared using metal titanium sheet as substrates by anodization and hydrothermal reaction methods. The photoelectrocatalysis reaction resistance (R = k/J_sph+R₀ = R₁+R₀) was measured by simple photoelectrochemical method, and used to express the electron transport characteristics of the nanotubular TiO₂ electrode. The overall resistance was found to consist of a variant （R₁） and an invariant component （R₀）. The R₁ was found to be inversely proportional to the saturation photocurrent and depends on the experimental conditions. The proportional constant, k, represents the minimum applied potential bias required to remove 100% of the photogenerated electrons from the photocatalyst layer and was found to be independent of the anodization time. The invariant component of the resistance （R₀） is an inherent property of the semiconductor photocatalyst that represents the sum of ohmic contact impedance at the conducting substrate/TiO₂ interface and crystalline boundaries impedance. The real saturated photocurrent density (J_real-sphd) was found to be independent of R₀ indicating the electron collection efficiency is independent of nanotube length. By controlling hydrothermal reaction conditions, e.g., starting TiO₂ crystalline type, alkali solution concentration, and reaction temperature, three-dimensional network TiO₂ nanotube film and TiO₂ nanobelt array film electrodes can be obtained. The resulting TiO₂ nanostructured electrodes have significant potentials in DSSCs, photoelectrocatalytic oxidation of water, and photoelectrocatalytic oxidation of organic matters. The fabricated TiO₂ nanostructured electrodes can not only solve the issues of powder photocatalyst loss, separation, and recovery, but also improve photocatalytic activity of the electrodes by coupling photocatalysis with electrochemical technology.更多还原